The present invention relates to heat pipes and, more particularly, to a control apparatus for heat pipes to allow heat flow from a piece or assembly to a sink and to prevent heat flow from a sink back to the piece or assembly.
Heat pipes operate to transfer heat from a relatively high temperature environment, such as would ordinarily be found within an electronic housing to a relatively low temperature area, such as would be present outside the housing. Transfer of heat in a heat pipe is effected by movement of vapor, produced by heating liquid in the inner portion of the pipe which is contained in the housing into the outer portion of said pipe which is positioned exteriorly of said housing, for radiation thereby. The outer portion of the heat pipe, being cooler, will condense the vapor and return it, as liquid, to the inner portions by capillary action, as by a wick, for revaporization and repetition of the cycle. If it is desired to "control" the heat pipe, such control may be effected either by varying the vapor flow through the pipe or by varying the flow of liquid through the wick, or both.
Various devices have been employed to control flow in heat pipes. One device which has been used is a pump to move cooling fluid to a heat sink with subsequent shutting down of the pump when isolation is desired. The disadvantage of using pumps, however, is that power is required and also additional weight is added. Particularly in an aircraft, both power and weight are critical items.
In U.S. Pat. No. 3,414,050, entitled, "Heat Pipe Control Apparatus", which issued Dec. 3, 1968, to Davinder K. Anand, a disk type damper valve is provided for controlling vapor flow. A wick is provided in the heat pipe and a movable wick segment is used to control liquid flow. The damper valve includes a fixed disk having spaced apertures and a movable disk pivotally connected to the fixed disk. A bellows which is operated by gas pressure from a tank is used to rotate the movable disk relative to the fixed disk.
Another mechanically operated valve for a heat pipe is shown and described in U.S. Pat. No. 3,489,203, entitled, "Controlled Heat Pipe", which issued Jan. 13, 1970, to Robert E. Fischell. In this patent, one embodiment is shown having a butterfly valve in the pipe and a bimetallic spring thermostat is used for actuating the butterfly valve thereby controlling the flow of vapor in the heat pipe.